U.S. patent application number 11/304732 was filed with the patent office on 2006-06-22 for image heating apparatus.
This patent application is currently assigned to CANON KABUSHIKI KAISHA. Invention is credited to Yasuyuki Aiko, Kenji Fukushi, Takamitsu Hirayama, Hidehiko Kinoshita, Hiroto Nishihara, Tomoichiro Ohta, Manabu Yamauchi.
Application Number | 20060131301 11/304732 |
Document ID | / |
Family ID | 36594392 |
Filed Date | 2006-06-22 |
United States Patent
Application |
20060131301 |
Kind Code |
A1 |
Ohta; Tomoichiro ; et
al. |
June 22, 2006 |
Image heating apparatus
Abstract
An image heating apparatus includes magnetic flux generating
means; a heat generating element for generating heat by a magnetic
flux generated by the magnetic flux generating means, the heat
generating element being effective to heat an image on a recording
material; electric power supplying means for supplying electric
power to the magnetic flux generating means; electric power
changing means for changing electric power to be supplied to the
magnetic flux generating means on the basis of a temperature rise
property of the heat generating element, in a period from start of
electric power supply to the magnetic flux generating means to
reaching of a temperature of the heat generating element to a
predetermined level.
Inventors: |
Ohta; Tomoichiro;
(Kashiwa-shi, JP) ; Yamauchi; Manabu;
(Kashiwa-shi, JP) ; Nishihara; Hiroto;
(Toride-shi, JP) ; Fukushi; Kenji; (Toride-shi,
JP) ; Aiko; Yasuyuki; (Toride-shi, JP) ;
Kinoshita; Hidehiko; (Kashiwa-shi, JP) ; Hirayama;
Takamitsu; (Abiko-shi, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Assignee: |
CANON KABUSHIKI KAISHA
TOKYO
JP
|
Family ID: |
36594392 |
Appl. No.: |
11/304732 |
Filed: |
December 16, 2005 |
Current U.S.
Class: |
219/619 ;
399/328 |
Current CPC
Class: |
G03G 2215/2035 20130101;
G03G 15/205 20130101; H05B 6/145 20130101 |
Class at
Publication: |
219/619 ;
399/328 |
International
Class: |
H05B 6/14 20060101
H05B006/14; G03G 15/20 20060101 G03G015/20 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 20, 2004 |
JP |
367623/2004(PAT.) |
Claims
1. An image heating apparatus comprising: magnetic flux generating
means; a heat generating element for generating heat by a magnetic
flux generated by said magnetic flux generating means, said heat
generating element being effective to heat an image on a recording
material; electric power supplying means for supplying electric
power to said magnetic flux generating means; and electric power
changing means for changing electric power to be supplied to said
magnetic flux generating means on the basis of a temperature rise
property of said heat generating element, in a period from start of
electric power supply to said magnetic flux generating means to
reaching of a temperature of said heat generating element to a
predetermined level.
2. An apparatus according to claim 1, wherein said heat generating
element is detachably mountable to said apparatus, and wherein said
apparatus is capable of being loaded with two heat generating
elements having different temperature rise properties.
3. An apparatus according to claim 1, further comprising
temperature detecting means for detecting a temperature of said
heat generating element, wherein said electric power changing means
changes the electric power to be supplied to said magnetic flux
generating means on the basis of a result of detection of said
temperature detecting means after a predetermined period elapses
from the start of the electric power supply to said magnetic flux
generating means.
4. An apparatus according to claim 1, wherein when the temperature
of said heat generating element after the predetermined period is
lower than a predetermined level, the electric power supplied to
said magnetic flux generating means is made higher, and when the
temperature is higher, the electric power supplied to said magnetic
flux generating means is made lower.
Description
FIELD OF THE INVENTION AND RELATED ART
[0001] The present invention relates to an image heating apparatus
which heats an image on recording medium with the use of an
inductive heating method. More specifically, it relates to an image
heating apparatus which employs an inductive heating method and is
suitable as an apparatus for adding gloss to an image on recording
medium, and also, a fixing apparatus.
[0002] Japanese Laid-open Patent Application 2000-39796 discloses
an image heating apparatus, as a fixing apparatus, which uses, as
the material for its heating member, a magnetic conductor
(substance in which heat is generated by electromagnetic
induction), the Curie point of which equals the fixation
temperature of the heating apparatus. As a magnetic conductor is
heated close to its Curie point, it increases in specific heat; it
increases in internal energy. Thus, as a magnetic conductor is
heated past its Curie point, it loses its spontaneous
magnetization, preventing thereby heat from being generated
therein. Therefore, by using a magnetic conductor, as the material
for the heating member, the Curie point of which equals the
temperature level necessary for image fixation, it is possible to
make the heating member control itself in temperature so that as
the temperature of the fixation roller rises close to the fixation
temperature, which equals the Curie point of the magnetic conductor
used as the material for the heating member, the heating member
automatically stops increasing in temperature.
[0003] Japanese Laid-open Patent Application 2000-39797 proposes a
fixing apparatus which heats an image on recording medium by
heating its heating member by electromagnetic induction. The
heating member of this fixing apparatus is formed of a magnetic
conductor, the Curie point of which has been set so that the
saturation temperature of the magnetic conductor (fixation roller)
falls within a temperature range which is no less than the fixation
temperature, but, no more than the hot-offset start temperature.
Here, the saturation temperature of a magnetic conductor is the
temperature level which the magnetic conductor does not exceeds,
due to the above described characteristic of the fixation roller
(magnetic conductor) that it controls itself in temperature as it
is heated through electromagnetic induction. With the employment of
this design, not only is it possible to eliminate the problem that
the warmup time increases because the speed at which the heating
member (magnetic conductor) increases in temperature, decreases,
due to the phenomenon that as the temperature of the heating member
approaches the Curie point of the magnetic conductor, of which the
heating member is formed, but also, it is possible to prevent the
hot-offset.
[0004] The Curie point of a magnetic conductor can be changed by
changing its composition. For example, a desired Curie point can be
achieved by changing in composition (compositional modification), a
magnetic conductor composed of the combination of iron and nickel,
combination of iron, nickel, and chrome, etc. [0005] 1) The
following heating member has been known as a countermeasure for the
phenomenon that as multiple sheets of recording medium of a small
size are continuously conveyed through a fixing apparatus which
employs an inductive heating method, the out-of-sheet-path portions
of the heating member, that is, portions of the heating member of
the fixing apparatus, which are between the edges of the path of a
sheet of the small size and the corresponding edges of the path of
a sheet of recording medium of the largest size conveyable through
the fixing apparatus, abnormally increases in temperature. That is,
there has been known a heating member (fixation roller) formed of a
magnetic conductor, the Curie point of which has been adjusted to a
desired level (for example, its Curie point is set to a value which
is no less than fixation point and no more than high temperature
offset point, or no more than the highest point in temperature the
apparatus can withstand) (hereafter, such fixation roller may be
referred to as Curie point fixation roller). In order to prevent
this fixation roller from abnormally rising in temperature, this
heating member (fixation roller) takes advantage of one of the
properties of the magnetic conductor, of which it is made, that is,
the property that as the temperature of a magnetic conductor
increases close to the Curie point of the magnetic conductor, the
magnetic conductor reduces in the efficiency with which heat is
generated therein (this phenomenon hereafter may be referred to as
Curie point property). However, the Curie point is one of the
specific properties of a magnetic conductor having a Curie point.
Therefore, if a Curie point roller designed to have a specific
Curie point value is manufactured in a substantial numbers, they
will not be uniform in Curie point; the actual Curie points of some
of the rollers will be different from the preset Curie point.
Therefore, it is possible that a fixing apparatus will be fitted
with a Curie point fixation roller, the Curie point of which is
different from the preset one by the amount outside the tolerance
range. Further, a Curie point fixation roller itself sometimes
changes in Curie point value due to wear and/or deterioration,
making it therefore possible that it will deviate in Curie point
value by an amount outside the tolerance range. [0006] 2) In
reality, there are many types of a fixing apparatus, which are
changeable in fixation temperature, and therefore, many types of a
Curie point fixation roller, which are different in Curie point,
are available for each type of a fixing apparatus. As long as each
type of a fixing apparatus is fitted with a matching Curie point
fixation roller, there will be no problem. However, there are many
type of a Curie point rollers mountable in each type of a fixing
apparatus as described above. Therefore, it is possible that a
fixing apparatus is fitted with a fixation roller for a fixing
apparatus of a different type. [0007] 3) Some fixing apparatuses
are designed so that their fixation rollers can be easily exchanged
by a user, making it possible that a fixation roller for another
type of an image forming apparatus will be accidentally mounted by
a user. In such a case, a Curie point fixation roller meant for an
image forming apparatus of a different type is mounted.
[0008] In each of the above described cases 1)-3), a mismatch
occurs between the Curie point fixation roller and the control
system of the fixing apparatus, preventing therefore the fixation
process from being properly controlled.
SUMMARY OF THE INVENTION
[0009] Thus, the primary object of the present invention is to
provide a heating apparatus capable of determining whether or not a
heating member mounted therein is a correct one.
[0010] Another object of the present invention is to control the
process of heating a heating member, according to the
characteristic of the heating member in the heating apparatus
regarding temperature increase, in order to make the fixing
apparatus to optimally operate.
[0011] Another object of the present invention is to make it
possible to properly control the heating process, regardless of the
nonuniformity in the characteristic of a heating apparatus
regarding temperature increase.
[0012] Another object of the present invention is to make it
possible to properly control the heating process, even if a heating
member, which has been mounted in a fixing apparatus, does not
match in type with the fixing apparatus.
[0013] As for the typical structure of the image heating apparatus
in accordance with the present invention for achieving the above
described objects, the image heating apparatus which comprises: a
magnetic flux generating means; a heating member in which heat is
generated by the magnetic flux from the magnetic flux generating
means; and an electric power supplying means for supplying the
magnetic flux generating means with electric power, and which heats
an image on recording medium by the heat generated in the heating
member, is characterized in that it also comprises an electric
power changing means for changing the electric power supplied to
the magnetic flux generating means, according to the characteristic
of the heating member regarding its temperature increase, during
the period from when the magnetic flux generating means begins to
be supplied with electric power to when the temperature of the
heating member reaches a preset level.
[0014] These and other objects, features, and advantages of the
present invention will become more apparent upon consideration of
the following description of the preferred embodiments of the
present invention, taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a schematic drawing of the image forming apparatus
in the first embodiment of the present invention, showing the
general structure thereof.
[0016] FIG. 2 is a schematic front view of the partially cutaway
view of the fixing apparatus.
[0017] FIG. 3 is an enlarged schematic sectional view of the
essential portions of the fixing apparatus.
[0018] FIG. 4 is a schematic perspective view of the excitation
assembly.
[0019] FIG. 5 is a schematic exploded perspective view of the
induction heating coil and magnetic core.
[0020] FIG. 6 is a drawing for describing the portion of the
fixation roller, across which it is heated.
[0021] FIG. 7 is a block diagram of the control system of the
fixing apparatus which employs an inductive heating method.
[0022] FIG. 8 is a graph showing the profiles of various fixing
apparatuses different in Curie point, regarding the increase in
their temperature which occurs as they are started up (with amount
by which electric power is supplied being kept constant).
[0023] FIG. 9 is a graph showing the sequence for identifying the
type of the fixation roller in the heating apparatus, and the
sequence for switching the control of the heating apparatus
according to the identified type of the fixation roller in the
heating apparatus.
[0024] FIG. 10 is a flowchart of the control of the fixing
apparatus in accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiment 1
(1) Example of Image Forming Apparatus
[0025] FIG. 1 is a schematic drawing of the image forming apparatus
in this embodiment of the present invention, showing the general
structure thereof. The image forming apparatus in this embodiment
is a laser copying machine (printer) of the transfer type, which
employs one of the electrophotographic processes.
[0026] Designated by a referential symbol 101 is an
electrophotographic photosensitive member, as an image bearing
member, in the form of a rotatable drum (which hereinafter will be
referred to as photosensitive drum), which is rotationally driven
in the clockwise direction indicated by an arrow mark in the
drawing, at a preset peripheral velocity.
[0027] Designated by a referential symbol 102 is a charge roller as
a charging means, which uniformly charges the peripheral surface of
the rotating photosensitive drum 101, to preset polarity and
potential level.
[0028] Designated by a referential symbol 103 is a laser scanner,
which scans the uniformly charged peripheral surface of the
rotating photosensitive drum 101, with a beam of laser light L
which it outputs while modulating the beam of laser light L with
sequential digital video signals in accordance with the image
formation data; the peripheral surface of the photosensitive drum
101 is exposed by the laser scanner. As a result, an electrostatic
latent image, which matches the pattern in which the peripheral
surface of the photosensitive drum 101 has been exposed, is formed
on the peripheral surface of the photosensitive drum 101.
[0029] Designated by a referential symbol 104 is a developing
apparatus, which develops, normally or in reverse, the
electrostatic latent image on the peripheral surface of the
photosensitive drum 101 into a visible image formed of toner (which
hereinafter will be referred to simply as toner image).
[0030] Designated by a referential symbol 105 is a transfer roller
as a transferring means, which is kept pressed upon the peripheral
surface of the photosensitive drum 101 with the application of a
preset amount of pressure, forming a transfer nip T. To this
transfer nip T, a sheet P of recording medium is conveyed from an
unshown sheet feeding mechanism, with a preset control timing, and
the sheet P is conveyed through the transfer nip T while remaining
pinched between the transfer roller 105 and photosensitive drum
101. While the sheet P is conveyed through the transfer nip T, a
preset transfer bias is applied to the transfer roller 105, with a
preset control timing. As a result, the toner image on the
peripheral surface of the photosensitive drum 101 is
electrostatically transferred in a manner of being peeled away from
the photosensitive drum 101, onto one of the surfaces of the sheet
P of recording medium which is being conveyed through the transfer
nip T while remaining pinched between the roller 105 and drum
101.
[0031] After being conveyed out of the transfer nip T, the sheet P
of recording medium is separated from the peripheral surface of the
photosensitive drum 101, and is introduced as an object to be
heated, into a fixing apparatus 100, which fixes the unfixed toner
image on the introduced sheet P of recording medium to the sheet P,
with the application of heat and pressure, turning thereby the
unfixed toner image into a permanent image, and discharges the
sheet P therefrom.
[0032] Designated by a referential symbol 106 is a cleaning device
for cleaning the photosensitive drum 101, which is for removing the
transfer residual toner, that is, the toner remaining on the
peripheral surface of the photosensitive drum 101 after the
separation of the sheet P of recording medium from the peripheral
surface of the photosensitive drum 101. After the cleansing of the
peripheral surface of the photosensitive drum 101, that is, the
removal of the transfer residual toner from the peripheral surface
of the photosensitive drum 101, the peripheral surface of the
photosensitive drum 101 is used for the following image
formation.
(2) Fixing Apparatus 100
[0033] The fixing apparatus 100 is an image heating apparatus which
uses the inductive heating method in accordance with the present
invention. FIG. 2 is a partially cutaway schematic front view of
this fixing apparatus 100, and FIG. 3 is an enlarged schematic view
of the essential portions of the fixing apparatus 100.
[0034] Designated by a referential symbol 1 is a fixation roller as
a heat generating member (heating member) in the form a hollow
cylinder, and designated by a referential symbol 2 is an elastic
pressure roller as a pressure applying member. The two rollers 1
and 2 are disposed in parallel, with the fixation roller 1
positioned above the pressure roller 2. The two rollers 1 and 2 are
kept pressed upon each other, forming a fixation nip N (heating
nip). Designated by a referential symbol 3 is an excitation
assembly, which is disposed in the hollow of the fixation roller 1;
the excitation assembly 3 is inserted into the fixation roller
1.
[0035] The fixation roller 1 is made up essentially of a sleeve 1a
as the main portion thereof, and a surface layer 1b coated on the
peripheral surface of the sleeve 1a. The sleeve 1a is roughly 300
.mu.m in thickness, and is formed of a magnetic conductor, more
specifically, an iron alloy (Fe--Cr--Ni), composed so that its
Curie point became a temperature level of TR3, which is higher by a
preset value than the fixation temperature TR2 (fixation-possible
temperature level), that is, the image heating temperature of this
apparatus. In other words, the fixation roller 1 is a Curie point
roller. The fixation roller 1 may be provided with an elastic layer
or the like, in addition to the surface layer 1b which functions as
a toner releasing layer. The Curie point TR3 of this fixation
roller 1 has been set to be higher than the fixation temperature
and below the hot offset start point. The upper limit for the Curie
point of the fixation roller 1 may be set to be no higher than the
highest temperature which the heating apparatus can withstand. For
example, the Curie point may be set to be no higher than the
highest temperature (230.degree. C.) which the sheath of the
excitation coil can withstand. With the Curie point of the fixation
roller 1 set to such a temperature level, it is possible to prevent
the apparatus from becoming damaged due to the abovementioned
abnormal increase in the temperature of the fixation roller.
[0036] This fixation roller 1 is rotatably supported by the rear
and front lateral plates 21 and 21 of the fixing apparatus, with a
pair of bearings 22 and 22 placed between the lengthwise ends of
the fixation roller 1, one for one.
[0037] As for the pressure roller 2, it is made up of a metallic
core 2a, a heat resistant elastic layer 2b, and a toner releasing
surface layer 2c. It is disposed under the fixation roller 1, in
parallel to the fixation roller 1. It is rotatably supported by the
rear and front lateral plates 21 and 21 of the fixing apparatus,
with a pair of bearings 23 and 23 placed between the lengthwise
ends of the pressure roller 2, and rear and front lateral plates 21
and 21,one for one. The bearings 23 and 23 are attached to the
lateral plates 21 and 21 so that they can be movable in the
direction perpendicular to the axial line of the fixation roller 1.
Further, the bearing 23 and 23 are kept pressed upward with the use
of unshown pressure applying means such as compression springs,
pressing thereby the pressure roller 2 upon the downwardly facing
portion of the peripheral surface of the fixation roller 1 with the
application of preset amounts of pressure F and F, against the
resiliency of the elastic layer 2b so that the fixation nip N,
shown in FIG. 3, having a preset width in the sectional view in
FIG. 3.
[0038] Designated by a referential symbol G is a gear for driving
the fixation roller 1, which is firmly attached to the lengthwise
rear end of the fixation roller 1. As driving force is transmitted
to this gear G from a driving force source M, the fixation roller 1
is rotated in the clockwise direction in FIG. 3, at a preset
peripheral velocity. As the fixation roller 1 is rotated, the
pressure roller 2 is rotated by the torque transmitted to the
pressure roller 2 from the fixation roller 1 by the friction which
occurs between the two rollers 1 and 2, in the fixation nip N.
[0039] The excitation assembly 3 is inserted into the hollow of the
fixation roller 1, being firmly supported between and by the rear
and front supporting members 24 and 24, with the lengthwise front
and rear ends of the excitation assembly 3 firmly attached to the
supporting members 24 and 24, so that a preset amount of gap is
created and maintained between the internal surface of the fixation
roller 1 and the excitation assembly 3, and also, so that the
excitation assembly 3 is positioned at a preset angle in terms of
the rotational direction of the fixation roller 1.
[0040] FIG. 4 is a schematic perspective view of the excitation
assembly 3, and FIG. 5 is an exploded schematic perspective view of
the combination of the induction heating coil and the magnetic
core, as a magnetic flux generating means. The excitation assembly
3 in this embodiment is an assembly made up of a holder 4, an
induction heating coil 5 (excitation coil) as an exciting means, a
magnetic core 6, a stay 7, etc.
[0041] The holder 4 is in the form of a trough, the cross section
of which is semicircular. Its external diameter is slightly smaller
than the internal diameter of the fixation roller 1. Within the
hollow of the holder 4, the induction heating coil 5 and magnetic
core 6 are held. The holder 4 is formed of a substance, which is
not only heat resistant, but also, has a substantial amount of
mechanical strength; for example, PPS resin which contains glass
fiber. Obviously, it is nonmagnetic. As for the substances suitable
as the material for the holder 4, there are PPS resin, PEEK resin,
polyimide resin, polyamide resin, polyamide-imide resin, ceramic,
liquid polymer, fluorinated resin, and the like.
[0042] The induction heating coil 5 as an exciting means must be
capable of generating an alternating magnetic flux strong enough
for heating. Thus, it must be low in electrical resistance and high
in inductance. As the core wire of the inductive heating coil 5,
Litz wire is used, which is made up of roughly 80-160 strands of
fine wires, the diameter of which is in the range of 0.1-0.3 mm,
which are bound together. As the fine wire, electrical wire covered
with insulating substance is used. The Litz wire is wound 8-12
times around the magnetic core 6, making up the induction heating
coil 5, so that the portion of the contour of the induction heating
coil 5, which faces the bottom portion of the internal surface of
the holder 4, matches in curvature the contour of the internal
surface of the holder 4. Since the Litz wire is wound around the
magnetic core 6 which is rectangular, the resultant induction
heating coil 5 has a shape resembling that of a long boat. The
induction heating coil 5 is disposed in the hollow of the holder 4,
in a manner of being fitted into the holder 4. Designated
referential symbols 5a and 5b are lead wires extended outward of
the holder 4, from the above described induction heating coil
5.
[0043] The magnetic core 6 is formed of such a magnetic substance
as ferrite or Permalloy, which is high in magnetic permeability and
low in residual magnetic flux density. It functions to guide the
magnetic flux generated by the induction heating coil 5, to the
sleeve 1a of the fixation roller 1, which is formed of one of the
aforementioned magnetic conductors. The magnetic core 6 in this
embodiment is T-shaped in cross section. It is the combination of
two magnetic portions: the portion which is comparable to the
horizontal portion of a letter T, and the portion which is
comparable to the vertical portion of a letter T.
[0044] The stay 7 is formed of a resin or a metallic substance,
which is nonmagnetic. It is rigid and is in the form of a long and
narrow plate. It is firmly attached to the holder 4 in a manner of
covering the opening of the holder 4 in which the induction heating
coil 5 and fixation roller 1 are disposed. As described above, the
excitation assembly 3 is inserted into the hollow of the fixation
roller 1, and is firmly supported between and by the rear and front
supporting members 24 and 24, by the rear and front lengthwise
ends, so that a preset amount of gap is created and maintained
between the internal surface of the fixation roller 1 and the
excitation assembly 3, and also, so that the excitation assembly 3
is positioned at a preset angle in terms of the rotational
direction of the fixation roller 1.
[0045] With the provision of the above described structural
arrangement, as the driving force source M is started, the fixation
roller 1 is rotated, and the pressure roller 2 is rotated by the
rotation of the fixation roller 1. While the two rollers 1 and 2
are rotating, the induction heating coil 5 is provided with
alternating electric current (high frequency electric current), the
frequency of which is in the range of 20 kHz-500 kHz, through the
pair of lead wires 5a and 5b extending from an electric power
source 31, as an electric power supplying means, for induction
heating. As the induction heating coil 5 is supplied with
alternating current, it generates an alternating magnetic flux.
This alternating magnetic flux is guided by the magnetic core 6 to
the sleeve 1a of the fixation roller 1, which is formed of a
magnetic conductor, being thereby applied thereto. As the
alternating magnetic flux is applied to the sleeve 1a, eddy current
is induced in the sleeve 1a. This eddy current generates heat
(Joule heat) in the wall of the sleeve 1a; the sleeve 1a is heated
by electromagnetic induction. As a result, the fixation roller 1
increases in temperature.
[0046] The fixing apparatus 100 is structured so that because of
the shape in which the fine wires of the induction heating coil 5
is wound, only the portions of the fixation roller 1, which are
directly facing the induction heating coil 5, are heated by the
magnetic flux generated by the excitation assembly 3. Referring to
FIG. 6, in this embodiment, only the portions of the fixation
roller 1, which are in the two areas of the adjacencies of the
peripheral surface of the induction heating coil 5, more
specifically, ranges D and E in FIG. 6, are heated. Therefore, the
fixing apparatus is controlled so that when the fixing apparatus is
started up, or while a sheet P of recording medium is conveyed
through the fixing apparatus, the heating of the fixation roller 1
is preceded by the starting of the rotation of the fixation roller
1, preventing thereby the problem that the surface temperature of
the fixation roller 1 becomes nonuniform in terms of the rotational
direction of the fixation roller 1, that is, the problem that high
temperature spots are created (certain ranges of the peripheral
surface of the fixation roller 1, in terms of the rotational
direction of the fixation roller 1, become substantially higher in
temperature than the rest. In this embodiment, the excitation
assembly 3 is angled, in terms of the rotation direction of the
fixation roller 1, so that the heating range D, that is, one of the
ranges in which the fixation roller 1 is heated, coincides in
position with the fixation nip N. As for the other heating range E,
first and second temperature detection elements TH1 and TH2
(temperature sensors) as temperature detecting means for detecting
the surface temperature of the fixation roller 1 are disposed in
this range. The information regarding the surface temperature of
the fixation roller 1 detected by the first and second temperature
detection elements TH1 and TH2 is inputted into a controller 32 as
an electric power application controlling means. The first and
second temperature detection elements TH1 and TH2 as temperature
detecting means will be described later.
[0047] The controller 32 controls the amount by which electric
power is supplied from the induction heating power source 31 to the
induction heating coil 5, based on the information regarding the
surface temperature of the fixation roller 1 inputted from the
first temperature detection element TH1, so that the surface
temperature of the fixation roller 1 is maintained at a preset
fixation temperature TR2.
[0048] With the surface temperature of the fixation roller 1 kept
at the preset fixation temperature, a sheet P of recording medium
(which hereinafter will be referred to simply as recording sheet
P), as an object to be heated, onto which an unfixed toner image t
have been transferred from the image forming means, is introduced
into the fixation nip N, and is conveyed through the fixation nip
N, with the sheet P remaining pinched between the fixation roller 1
and pressure roller 2. As a result, the unfixed toner image t on
the recording sheet P is fixed to one of the surfaces of the
recording sheet P by the heat from the fixation roller 1 and the
pressure in the fixation nip N.
[0049] Referring FIG. 2, designated by a referential symbol A is
the path of a recording sheet P, which is the largest in terms of
the direction perpendicular to the recording sheet conveyance
direction. Designated by a referential symbol B is the path of a
recording sheet P, which is smaller in width than the largest
recording sheet. Incidentally, in this embodiment, a recording
sheet P is conveyed through the fixing apparatus so that the center
of the recording sheet P coincides with the lengthwise center of
the fixation roller 1; designated by a referential symbol O is the
referential line which coincides with the center of the recording
sheet P. Designated by referential symbols B' and B' are the areas
between the lateral edges of the path B of the small recording
medium P and the lateral edges of the path A of the largest
recording medium, that is, the portions of the path A of the
largest recording medium, with which the small recording medium
does not come into contact with as it is conveyed through the
fixing apparatus.
[0050] The first temperature detection element TH1 is disposed in
contact, or almost in contact, with the portion of the fixation
roller 1, which is within the path B of the small recording medium,
whereas the second temperature detection element TH2 is disposed in
contact, or almost in contact with, one of the portions of the
fixation roller 2 which are within the portions B' of the path A of
the largest recording medium.
[0051] When multiple small recording mediums P are continuously
conveyed through the fixing apparatus, the portions of the fixation
roller 1, which are in the portions B' of the path A of the largest
recording medium, increase in temperature beyond the preset
fixation temperature TR2. However, as the temperature of these
portions of the fixation roller 1 increases past a permeability
changing point, which is lower than the Curie point TR3 of the
fixation roller 1, the fixation roller 1 begins to reduce in the
efficiency with which heat is generated therein. Consequently, the
temperature of these portions of the fixation roller 1 converges to
the Curie point TR3, at which the permeability of the fixation
roller 1 is 1; in other words, the temperature of these portions of
the fixation roller 1 are prevented from increasing in temperature
beyond the Curie point TR3 (portions of fixation roller outside
recording medium path controls themselves in temperature). In this
embodiment, the Curie point TR3 of the fixation roller 1 is set to
be lower than the hot-offset starting point, preventing thereby the
hot-offset attributable to the excessive increase in temperature of
the portions of the fixation roller 1, which are in the portions B'
and B', that is, the out-of-recording medium path, of the path A of
the largest recording medium.
(3) Structure of Fixation Control System
1) Basic Control
[0052] FIG. 7 is a block diagram of the fixation control system of
the fixing apparatus employing the above described inductive
heating method.
[0053] Designated by a referential symbol 31 is an induction
heating power source (excitation circuit, electric power applying
means, electric power converting apparatus), which supplies
alternating electric current to the induction heating coil 5, as an
exciting means, of the excitation assembly 3 disposed (inserted) in
the hollow of the fixation roller 1 as a heating member. In other
words, the induction heating power source 31 as an electric power
supplying means is such an electric power supplying means that is
capable of varying in frequency and amplitude the electric power
supplied to the induction heating coil 5 to heat the fixation
roller 1.
[0054] Designated by a referential symbol 32 is the controller as
an electric power controlling means, which varies the amount by
which the above described induction heating power source 31
supplies electric power to the induction heating coil 5 (electric
power conversion control).
[0055] In the induction heating power source 31, designated by a
referential symbol TR1 is an electric power switching element made
up of an IGBT or a MOS-FET, and designated by a referential symbol
C2 is a resonant capacitor for converting the waveform of the high
frequency alternating current applied to the induction heating coil
5 as a load, into the resonant waveform. Designated by a
referential symbol D5 is a flywheel diode for regenerating the
electric power stored in the induction heating coil 5.
[0056] As described above, the first and second temperature
detection elements TH1 and TH2, respectively, are positioned in the
heating range E (FIG. 6), which is one of the heating ranges which
are highest in the amount by which heat is generated in the wall of
the fixation roller 1 (1a), being thereby thermally closely tied to
the fixation roller 1. As the first and second temperature
detection elements TH1 and TH2, it is common practice to employ
so-called thermosensitive resistors such as a thermistor. Their
outputs are inputted into a temperature detection circuit IC2,
which outputs voltages, the values of which are proportional to the
changes in the electric resistance of the temperature detection
elements TH1 and TH2. The outputs from the temperature detection
circuit IC2 are inputted into the controller 32.
[0057] The output of the first temperature detection element TH1 is
inputted as a temperature signal T-MON into the controller 32,
which controls the resonance control circuit IC1 of the induction
heating power source 31, based on the output of the first
temperature detection element TH1.
[0058] The controller 32 controls the operation for supplying the
fixation roller 1 of the fixing apparatus 100 with electric power,
according to the operational state (whether it is in startup
process, actually copying, on standby, or another process) of the
copying machine; it controls the timing with which the fixing
apparatus is supplied with electric power, and the amount by which
the fixing apparatus is supplied with electric power.
[0059] The resonance control circuit IC1 has a one-shot pulse
generation circuit 33, a comparison circuit 34. To the one-shot
pulse circuit IC1, a power command value P.sub.cont (target amount
for electric power) is inputted from the controller 32. To the
comparison circuit 34, an operation authorization signal for
controlling the oscillating operation itself of the resonance
control circuit IC1 is inputted. After being inputted into the
resonance control circuit IC1, the power command value P.sub.cont
is inputted as a power control signal into the pulse modulation
(which hereinafter will be referred to as PFM) oscillation circuit
in the resonance control circuit IC1. The resonance control circuit
IC1 generates a PFM pulse which matches the power command value
P.sub.cont, and outputs it to the gate of the electric power
switching element TR1, driving thereby the electric power switching
element TR1.
[0060] Designated by a referential symbol AC is a commercial
alternating current power source. The electric power inputted from
this power source AC into the input terminals a and b of the
induction heating power source 31 is rectified by an input power
rectification circuit 35 made up of diodes D1-D4 connected in the
bridging fashion, and then, is flowed through a smoothing circuit
36 (noise filter) made up of an input noise filter NF1 and a
smoothing condenser C1, being thereby supplied as pulsating
current, which results from the rectification of alternating
current, to a power control circuit portion. The smoothing circuit
36 is set to such a constant that ensures that the switching
frequency of the electric power switching element TR1 is attenuated
by a sufficient amount, whereas the electric power source frequency
passes without being attenuated.
[0061] Designated by a referential symbol 37 is a current detection
transformer (CT1). Designated by a referential symbol 38 is a coil
current detection circuit, which detects the amount of current
flowing from the induction heating power source 31 to the induction
heating coil 5, and inputs the results of the detection to the
controller 32. The controller 32 computes the amount P.sub.coil of
the power supplied to the coil 5, based on this amount of current
detected by the coil current detection circuit 38.
[0062] Designated by a referential symbol 39 is a current detection
transformer (CT2). Designated by a referential symbol 40 is a coil
current detection circuit, which detects the amount of the current
flowing from the commercial alternating current power source to the
induction heating power source 31, and inputs the detected amount
into the controller 32, which computes the amount of the inputted
amount of power, based on the detected amount of the current.
[0063] Next, the operation of the fixation control system will be
described. As the controller 32 receives a heating start signal
(signal for starting up fixing apparatus) at the starting of a
copying operation, it outputs the operation authorization signal
IH-ON and power command value P.sub.cont, to the resonance control
circuit IC1 of the induction heating power source 31, according to
the operational state of the copying machine. As a result, the
resonance control circuit IC1 outputs a high frequency PFM
signal.
[0064] In other words, an alternating current input voltage is
applied to the input terminals a and b of the induction heating
power source 31. As the alternating current input voltage is
applied to the induction heating power source 31, the voltage is
rectified by the current rectifying elements D1-D4 of the input
power rectification circuit 35, into pulsating current, the voltage
of which is applied to the terminals of the by-pass condenser C1
(smoothing condenser) through the input noise filter NF1 of the
smoothing circuit 36. Therefore, the voltage between the terminals
of the bypass condenser C1 has the waveform resulting from the
rectification of the inputted alternating current voltage.
[0065] From the controller 32, a preset power command value
P.sub.cont is applied as a control signal to the PFM oscillation
circuit of the resonance control circuit IC1. The resonance control
circuit IC1 generates and outputs a PFM signal, the pulse of which
matches that of the control signal. This output from the resonance
control circuit IC1 is applied between the gate sources of the
power switching element TR1, turning on the power switching element
TR1. As a result, drain current ID flows, supplying thereby the
induction heating coil 5 with power.
[0066] The current which flows as the power switching element TR1
is turned on is stored in the induction heating coil 5. Therefore,
as the power switching element TR1 is turned off, the induction
heating coil 5 generates such voltage that is opposite in polarity
to the current which was being supplied to the induction heating
coil 5. As a result, the resonance condenser C2 is charged by the
electric power which has been stored in the induction heating coil
5. In other words, the voltage of the resonance condenser C2 is
increased by the current which flows into the condenser C2 from the
induction heating coil 5 which has been storing electric power.
[0067] The current which flows out of the induction heating coil 5
attenuates in reverse proportion to the increase in the voltage of
the resonance condenser C2, eventually stops flowing. As soon as
current stops flowing from the induction heating coil 5, the
electrical charge having accumulated in the resonance condenser C2
begins to move toward the induction heating coil 5; electric
current begins to flow toward the induction heating coil 5.
[0068] Thereafter, at the same time as the electric charge having
been stored in the resonance condenser C2 returns to the induction
heating coil 5, the oscillation voltage drops. At the point in time
at which the electric charge having been stored in the resonance
condenser C2 completely discharges, current is flowing again
through the induction heating coil 5 in the reverse direction.
Therefore, the drain voltage of the power switching element TR1 is
rendered lower than the source voltage, by this voltage which is
reverse in polarity. As a result, the flywheel diode D5 is turned
on, allowing thereby current to flow in the forward direction.
[0069] After a certain length of time, an on-signal is supplied to
the power switching element TR1, turning on the power switching
element TR1. As the power switching element TR1 is turned on,
current flows forward in the induction heating coil 5, and
accumulates in the induction heating coil 5. The above described
sequence is repeated. As a result, current is induced in the
fixation roller 1 (1a), which is in the immediate adjacencies of
the induction heating coil 5 and constitutes a load which is
electromagnetically connected to the induction heating coil 5.
Consequent, the fixation roller 1 (1a) formed essentially of a
magnetic conductor generates heat (Joule heat) by the amount equal
to the product between the electrical resistance of the fixation
roller 1 (1a) and the square of the amount of the current induced
in the fixation roller 1 (1a). In other words, the wall of the
fixation roller 1 is efficiently heated from within. Since the
fixation roller 1 is being rotated, it is heated in its
entirety.
[0070] In this fixation control system, the high frequency
component of the current which flows through the switching element
TR1 and induction heating coil 5L1 is smoothed by the bypass
condenser C1 through charging and discharging processes. Therefore,
high frequency current does not flow to the input noise filter NF1;
only alternating current which is identical in waveform to the
inputted alternating current flows through the input noise filter
NF1.
[0071] The current which flows through the rectification diode
D1-D4 of the input power rectification circuit 35 turns into the
current waveform, which is effected as the current waveform having
flowed through the switching element TR1 and induction heating coil
5 is filtered by the smoothing circuit 36 made up of the bypass
condenser C1 and input noise filter NF1. Therefore, the waveform of
the alternating input current turns into an input current waveform
which closely resembles the waveform of the alternating input
current. Therefore, the high frequency component in the input
current is substantially reduced, which results in the substantial
improvement, in power factor, of the input current of the induction
heating power source 31.
[0072] The input noise filter NF1 and bypass condenser C1 which
make up the smoothing circuit 36 in this circuit have only to be
effective to filter the high frequency component of the current
from the resonance control circuit IC1. Therefore, the bypass
condenser C1 and input noise filter NF1 may be reduced in capacity
and inductance, respectively, making it possible to reduce the
circuit in size and weight.
[0073] Into the induction heating power source 31 designed as
described above, the power command value P.sub.cont is inputted
from the controller 32. Therefore, high frequency alternating
electric power, the frequency of which is in the range of 20 kHz-1
MHz, can be generated at the output terminals c and d of the
induction heating power source 31.
[0074] The outputs of the first and second temperature detection
elements TH1 and TH2 for measuring the surface temperature of the
fixation roller 1 are continuously inputted into the temperature
detection circuit IC2, which converts the outputs of the
temperature detection elements TH1 and TH2 into temperature
signals, and outputs the temperature signals. The temperature
signals outputted from the temperature detection circuit IC2 are
inputted into the controller 32, which continuously compares the
surface temperature of the fixation roller 1 detected by the
temperature detection element TH1, with the target temperature. The
difference between the surface temperature of the fixation roller 1
detected by the temperature detection element TH1 and the target
temperature is fed back as the power command value P.sub.cont of
the resonance control circuit IC1.
[0075] The controller 32 internally stores the target surface
temperature for the fixation roller 1. As the surface temperature
of the fixation roller 1 detected by the first temperature
detection element TH1 increases close to this target temperature
stored in the controller 32, the controller 32 generates a feed
back signal for keeping constant the surface temperature of the
fixation roller 1. As for the method for keeping constant the
surface temperature of the fixation roller 1, such a control method
as the proportional control method, so-called PID control method,
or the like for reducing the amount by which high frequency power
is supplied to the induction heating coil 5 is employed.
[0076] The controller 32 computes the difference between the
surface temperature of the fixation roller 1 detected by the
temperature detection circuit IC2 and the target temperature for
the fixation roller 1, and outputs the difference as the power
command value P.sub.cont to the resonance control circuit IC1. The
resonance control circuit IC1 sets the length of time the gate of
the power switching element TR1 is to be kept turned on, based on
the inputted power command value P.sub.cont, adjusting thereby the
amount by which power is supplied to the power switching element
TR1. As a result, the power supplied to the induction heating coil
5 is controlled, and therefore, the amount by which heat is
generated in the wall of the fixation roller 1 is controlled.
Consequently, the temperature of the fixation roller 1 is
stabilized at the fixation temperature TR2.
2) Identification of Mounted Fixation Roller, and Control
Modification for Compensating for Difference Among Various Types of
Fixation Roller 1
[0077] As described above, in this embodiment, the fixing apparatus
is provided with the fixation roller 1, which is formed of a
magnetic conductor, the Curie point of which is higher than a
preset fixation temperature, and in the wall of which heat is
electromagnetically generated by the function of alternating
magnetic flux generated by the induction heating coil 5 to
thermally fix an unfixed image t on recording medium. Further, the
fixing apparatus is enabled to operate in the control modification
mode, in which while the fixation roller 1 is increased in
temperature during the startup period of the fixing apparatus, the
characteristic of the mounted fixation roller 1 regarding its
temperature increase is detected, and its power controlling method
is modified to accommodate the characteristic of the mounted
fixation roller 1 regarding temperature increase. More concretely,
while the fixation roller 1 is increasing in temperature during the
startup period of the fixing apparatus, the characteristic of the
mounted fixation roller 1 regarding temperature increase is
detected from the amount of the alternating current power supplied
to the induction heating coil 5, and the information regarding the
temperature detected by the first temperature detection element
TH1. Then, the amount by which power supplied to the induction
heating coil 5 is controlled according to the detected
characteristic of the fixation roller 1 regarding temperature
increase. Hereafter, this modification of the control method will
be described in detail.
[0078] Generally, a fixing apparatus which heats an object by
electromagnetic induction is provided with a fixation roller such
as the above described fixation roller 1, which is formed of a
magnetic conductor, the Curie point of which has been preset. Thus,
if a fixation roller which does not meet the tolerance in terms of
the Curie point is mounted in a fixing apparatus, or the fixation
roller mounted in a fixing apparatus is not the normal fixation
roller, that is, such a fixation roller that does not match in type
the fixing apparatus in which it is mounted, the fixation process
cannot be properly controlled.
[0079] The fixation roller 1 (1a) is formed of one of magnetic
conductors, for example, such an iron alloy as Fe--Cr--Ni, the
Curie point of which is in the adjacencies of the preset fixation
temperature. The magnetic conductors different in Curie point are
different in heat generation efficiency. That is, if a given
magnetic conductor is different in composition from another
magnetic conductor, the two are different in specific resistivity.
Therefore, the fixation rollers (1)-(4), which are different in
properties, more specifically, Curie point, are different in heat
generation profile, that is, the rate at which they increase in
temperature during the startup period, as shown in FIG. 8, provided
that they are the same in the amount by which they are supplied
with electric power. In other words, if fixation rollers different
in Curie point are supplied with electric power by the same amount,
that is, the amount corresponding to the electric power supply
command value computed based on the fixation roller temperature and
target fixation temperature, they become different in the length of
the startup time. For example, in the case of the aforementioned
iron alloy, the higher the Cr content, the higher in specific
resistivity and lower in Curie point, being therefore higher in the
ratio of the amount of the heat generated therein to the amount of
the electric current supplied to the induction heating coil 5 for
heat generation, compared to pure iron. This is for the following
reason. That is, if two fixation rollers are different in material,
the two are different in the amount of the load resistance of the
coil, as seen from the power source side. Therefore, even when the
two rollers are the same in the difference between their current
temperatures and target fixation temperatures, and also, the same
in the power supply command value, they are different in the actual
amount by which electric power is supplied to the induction heating
coil 5.
[0080] The fixation roller (1) has a metallic core formed of pure
iron, and therefore, its heat generation profile is basically the
same as that of pure iron, the Curie point of which is very high.
Therefore, it does not occur that within the temperature range in
which the fixation roller (1) is used, the temperature of the
fixation roller (1) reaches its Curie point. The fixation roller
(2) is a fixation roller, the Curie point of which is the same as
the preset Curie point TR3 of the fixation roller of the fixing
apparatus in this embodiment. In other words, the Curie point TR3
of this fixation roller (2) is higher by a preset amount than the
fixation temperature TR2.
[0081] The fixation roller (3) is a fixation roller, the Curie
point TR3' of which is higher than the fixation temperature TR2 of
the fixation roller (2), but is lower than the Curie point TR3 of
the fixation roller (2).
[0082] The fixation roller (4) is a fixation roller, the Curie
point TR3'' of which is lower than the fixation temperature TR2 of
the fixation roller (2).
[0083] The lower in Curie point the fixation roller
((1)-(2)-(3)-(4)), the higher in specific resistivity, compared to
iron, being therefore greater in the amount of the heat generated
therein by the electric current flowed to the induction heating
coil 5 for heat generation, being therefore greater in the gradient
at which its temperature increases during the startup period, being
therefore shorter in the length of the time for the temperature of
the fixation roller to rise the target fixation temperature TR2.
However, the Curie point TR3'' of the fixation roller (4) is lower
than the fixation temperature TR2 of the fixation roller (2).
Therefore, as the temperature of the fixation roller (4) rises
close to its Curie point TR3'', which is lower than the target
fixation temperature TR2, the fixation roller (4) enters the state
in which its temperature no longer rises; it controls itself in
temperature. Therefore, the temperature of the fixation roller (4)
never rises to the target fixation temperature TR2.
[0084] Therefore, there is the following relationship among the
fixation rollers (1)-(4), in terms of the temperature levels TR(a),
TR(b), TR(c), and TR(d), which they reach, respectively, during the
period from the point T0 in time at which electric power begins to
be supplied, to the point T in the startup period:
TR(a)<TR(b)<TR(c)<TR(d), respectively.
[0085] Therefore, the fixation rollers (1)-(4), which are different
in Curie point, can be identified using the above described
differences among them in their characteristics in temperature
increase during the startup period.
[0086] In this embodiment, the fixation roller 1 in a fixing
apparatus is identified using the above described criterion, during
a part of the control carried out when the fixing apparatus is
started up, that is, immediately after the fixing apparatus is
turned on. Then, even if the fixation roller in the fixing
apparatus happens to be a fixation roller which does not meet the
preset tolerance, or a fixation roller, the Curie point of which is
not the normal one for the type of the fixing apparatus, the amount
by which electric power is supplied to the fixation roller is
controlled so that it matches the Curie point of the fixation
roller in the fixing apparatus; in other words, it is made possible
for the fixing apparatus to be properly controlled.
[0087] Next, referring to FIG. 9, which is a diagram showing the
sequence for starting up the fixing apparatus in this embodiment,
and FIG. 10, which is a flowchart showing the control carried out
during the startup period, how the fixation roller in the fixing
apparatus is identified in type, and also, how the control carried
out during the start up period is modified according to the
identified type of a fixation roller, will be described.
[0088] Before the controller 32 starts an actual copying operation,
it starts the startup operation (START) for raising the temperature
of the fixation roller 1 to a preset level.
[0089] First, the controller 32 activates a timing means 32a as a
clocking means, and then, outputs a signal IH-ON for turning on the
induction heating power source 31, while clocking the elapsed
time.
[0090] The operation for heating the fixation roller 1 is started
by supplying the induction heating coil 5 with electric power
P.sub.coil, the pulse width of which is kept fixed to a pulse width
of P1 during this period.
[0091] As the clocking means 32a detects that a preset length of
time (which corresponds to point T1) has elapsed after the heating
of the fixation roller 1 is started, the controller 32 reads the
surface temperature TR of the fixation roller 1 through the first
temperature detecting means TH1.
[0092] If the detected temperature of the fixation roller 1 is no
less than TR(d), the controller 32 determines that the fixation
roller in the fixing apparatus is a fixation roller, the Curie
point of which is lower than the fixation temperature TR2. In this
case, the controller 32 determines that the fixation roller in the
fixing apparatus is not usable with the fixing apparatus, and stops
the apparatus (ERR-STOP). Then, it shows, on the display (unshown),
a warning message that prompts an operator to replace the fixing
apparatus. The temperature TR(d) is the surface temperature, at the
point T1 in time, of a fixation roller, the Curie point TR3'' of
which is lower than the preset fixation temperature TR2.
[0093] If the detected temperature TR of the fixation roller is
close to TR(b), the controller 32, as an electric power amount
changing means (means for adjusting amount by which electric power
is supplied to coil 5), determines that the fixation roller in the
fixing apparatus is the fixation roller (2), the Curie point of
which matches the fixing apparatus. In this case, the controller 32
continues the startup heating operation, in which the pulse width
of the electric power P.sub.coil applied to the coil 5 is the pulse
width P1.
[0094] If the detected temperature TR of the fixation roller is
close to TR(b), the controller 32, as the electric power amount
changing means, determines that the fixation roller in the fixing
apparatus is the fixation roller (1) (fixation roller having
metallic core formed of iron) which is not as good as possible in
terms of the rate of temperature increase during the startup
period. Then, based on this determination, the controller 32
increases the amount by which electric power is supplied to the
coil 5, to a preset value, by switching the pulse width of the
electric power supplied to the coil 5, to a pulse width P1(a).
[0095] If the detected temperature TR of the fixation roller is
close to TR(c), the controller 32 determines that the fixation
roller in the fixing apparatus is a fixation roller, the Curie
point of which is higher than the fixation temperature TR2 of the
fixation roller (2), but is lower than the Curie point TR3 of the
fixation roller (2). Then, based on this determination, the
controller 32 changes in pulse width the electric power P.sub.coil
supplied to the induction heating coil 5, reducing thereby the
amount by which electric power is supplied to the coil 5.
[0096] As described above, the type of the fixation roller 1 can be
identified by detecting the surface temperature TR of the fixation
roller 1 at the specific point T1 in time while the fixation roller
1 is increasing in surface temperature. Thus, by controlling the
amount by which electric power is supplied to the induction heating
coil 5, according to the identified type (roller material), the
fixation rollers (1), (2), (3), and (4) can be rendered uniform in
the length of time it takes for the surface temperature of the
fixation rollers (1), (2), (3), and (4) to reach the fixation
temperature TR2 during the startup period; they all reach the
fixation temperature TR2 at the same time of T2, as shown in FIG.
9, regardless of the material therefor, making it possible to
improve a copying machine, a printer, and the like, not only in
terms of energy conservation, and also, in terms of the actual
impression of being easy to use, because the apparatus does not
need to be stopped for fixation roller replacement.
[0097] Referring to FIG. 9, the pulse width P2 is the pulse width
of the electric power which begins to be supplied to the induction
heating coil 5 immediately after the completion of the startup
operation, in order to start a copying (printing) operation
immediately after the completion of the startup operation. In other
words, it is the pulse width of the electric power supplied to the
coil 5 while a sheet of recording medium is conveyed through the
fixation portion. The point T3 in time coincides with the point in
time at which the copying (printing) operation is ended, and at
which the pulse width of the electric power supplied to the coil 5
is reduced to the pulse width P2. In other words, the point T3 in
time at which the pulse width is reduced from the pulse width P2
coincides with the end of the copying operation.
[0098] The fixation roller 1 of the image heating apparatus in this
embodiment is removably mountable in the image heating apparatus,
and therefore, it is possible that one of the fixation rollers
different from the fixation roller 1 in this embodiment, in terms
of one of their characteristics, more specifically, the
characteristic regarding temperature increase, will be mounted in
the image heating apparatus. In other words, it is possible that a
fixation roller matching an image heating apparatus different in
type from the image heating apparatus in this embodiment will be
mounted in the image heating apparatus in this embodiment, creating
an unexpected combination of a fixing apparatus and the main
assembly of an image forming apparatus. In this embodiment,
however, even if such a combination as the above described one
occurs, that is, a mismatch occurs between the fixing apparatus 100
and image forming apparatus main assembly, the above described
characteristic of the fixation roller 1 regarding temperature
increase during the startup period can be easily detected.
Therefore, the problems which may be caused by the mismatch can be
prevented.
[0099] Incidentally, the Curie point of the fixation roller (1) is
higher than the Curie point TR3 of the normal fixation roller (2).
Therefore, when continuously conveying multiple recording mediums
of a small size, the controller 32 watches the temperature increase
of the portion of the fixation roller outside the recording medium
path of the recording medium being currently conveyed, with the use
of the second temperature detecting means TH2, and controls the
image forming operation so that the portion of the fixation roller
outside the recording medium path does not excessively increase in
temperature; more specifically, the controller 32 adjusts the
length of the recording medium intervals to prevent the temperature
of the portion of the fixation roller outside the recording medium
path, from exceeding the preset temperature limit of TR3.
[0100] Further, if the controller 32 detects that the temperature
of the fixation roller inputted from the first or/and second
temperature detecting means TH1 and TH2 has exceeded the preset
upper limit, it determines that a thermal runaway has occurred to
the image heating apparatus. Then, it immediately stops the
apparatus, and displays a message indicating the occurrence.
[0101] Incidentally, it is true that in this embodiment, even if
the fixation roller in the image heating apparatus is identified as
the fixation roller (1) or (3), the fixation roller in the image
heating apparatus is not replaced, and is used while being
controlled in temperature with the use of the electric power
controlling method matching the fixation roller in the image
heating apparatus. However, there is no doubt, in this case, that
the fixation roller in the image heating apparatus is a mismatch to
the image heating apparatus. Therefore, it is preferable that the
image forming apparatus is structured so that when there is this
kind of mismatch, a message prompting fixing apparatus replacement
is displayed. It is also possible to structure an image forming
apparatus so that if it is determined that the fixation roller in
the image heating apparatus is the fixation roller (1), the
operation is stopped, and a message prompting fixating apparatus
replacement is displayed, as it is if the fixation roller in the
fixing apparatus is determined to be the fixation roller (4).
[0102] Further, the referential temperatures TR(a), TR(b), and
TR(c) used for identifying in type various fixation rollers may be
replaced with referential temperature ranges, or a larger number of
referential temperatures. It is also possible to provide a
step-less temperature reference data so that a fixation roller can
be identified in type based on its temperature detected at the
point T1 in time.
[0103] As described above, the fixing apparatus in this embodiment,
which uses, as the material for its fixation roller 1, a substance
having its Curie point in the adjacencies of the fixation
temperature of the fixation apparatus, and also, uses
electromagnetic induction to heat the fixation roller 1, is
characterized in that it comprises the controller 32 (controlling
apparatus), and induction heating power source 31 (high frequency
power converting apparatus) which varies the amount of electric
power supplied to the induction heating coil 5 in response to a
command from the controller 31, and the controller 32 identifies in
type the fixation roller in the fixing apparatus, based on the
characteristic of the fixation roller regarding the temperature
increase during the startup period, and optimizes the amount by
which electric power is supplied to heat the fixation roller 1,
based on the identity of the fixation roller 1 in the image heating
apparatus.
[Miscellanies]
[0104] 1) The present invention is also applicable to such an image
heating apparatus of the induction heating type that is provided
with a magnetic flux blocking plate for preventing the portions of
a fixation roller outside the recording medium path from
excessively increasing in temperature, and a means for driving the
magnetic flux blocking means, in order to prevent such problems as
unsatisfactory fixation attributable to the mismatch in Curie point
between the image heating apparatus and its heating member. [0105]
2) An image heating apparatus may be structured so that the
excitation assembly 3 as an exciting means is disposed outside the
fixation roller 1 as a heating member. [0106] 3) Not only is the
image heating apparatus in accordance with the present invention
usable as the fixing apparatus in this embodiment, but also, as an
image heating apparatus for temporary fixation, a thermal
processing apparatus for improving, in surface properties such as
glossiness, a recording medium and the image borne thereon, by
reheating the recording medium and the image borne thereon, and the
like apparatuses.
[0107] While the invention has been described with reference to the
structures disclosed herein, it is not confined to the details set
forth, and this application is intended to cover such modifications
or changes as may come within the purposes of the improvements or
the scope of the following claims.
[0108] This application claims priority from Japanese Patent
Application No. 367623/2004 filed Dec. 20, 2004 which is hereby
incorporated by reference.
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